The present invention pertains to a device for printing printed sheets according to the screen printing method with a printing table and a screen mechanism arranged above it, with a screen frame and a conveying device for moving the printed sheets before, during and after printing.
Devices of the type described above have been known in the area of screen printing presses for a long time. They have proved, in principle, successful, but limits are set to the acceleration of the printing process because of the conveying means used. This arises from the fact that the individual printed sheets are grasped by grippers at the beginning of the screen printing press in devices known from the prior art and are then pulled onto the printing table. As soon as the printed sheet to be printed on has reached its correct position on the printing table, the screen frame arranged above the printing table is lowered in order to initiate the printing process. The gripping arms of the conveying means located at the level of the printed sheet must be lowered for this purpose. The gripping arms rise again after the printing operation in order to initiate the next work cycle. Especially the special movements of the gripping arms necessary within the printing mechanism can be accomplished only at an increased mechanical effort and they therefore cause rather substantial additional costs during the manufacture of such screen printing presses.
In addition, it is disadvantageous that the rapidity of the corresponding movements of the gripping arms is limited due to the heavy weights that must be moved.
The object of the present invention is therefore to improve a device for printing printed sheets according to the screen printing method such that the entire printing operation can be speeded up and that the design embodiment especially of the conveying device is substantially simplified and is made less expensive.
This object is accomplished according to the present invention with a device for printing printed sheets according to the screen printing method with a printing table and a screen mechanism arranged above it, with a screen frame and a conveying device for moving the printed sheets before, during and after printing. The conveying device has, when viewed in the conveying direction, at least one clamping device for clamping the lateral edge area of the printed sheets, which is arranged on the side of the printed sheets and is displaceable in the conveying direction. The clamping device has the shape of a continuous chain with individual gripper clamps fastened thereto.
Such a design embodiment avoids the need for additional mechanical movements, such as the lowering of the gripper or the like, so that more rapid conveying of the printed sheets can be achieved, on the whole, within the device. Moreover, there is sufficient space in the lateral area of the printed sheets to guarantee the reliable grasping of the sheets to be conveyed there.
It has proved to be particularly advantageous for the clamping device, which is arranged on the side of the printed sheets and which has at least one gripper clamp with an upper clamping jaw and a lower clamping jaw, to be fastened to an endless conveyor belt running on the side of the printing table. The endless conveyor belt guarantees the continuous movement of the clamping device, so that a return after the conveying of a printed sheet can take place due to the device according to the present invention at a level located below the printing table, the conveyor belt being guided by deflecting rollers. It is thus unnecessary to interrupt the conveying cycles to return the individual clamping devices.
An especially inexpensive design of the conveyor belt is obtained by using a roller chain, wherein the gripper clamps of the clamping device, which are advantageously used in a rather large number, are fastened to an individual chain link each.
Corresponding to an expedient embodiment, the clamping jaws of the gripper clamps are held in the clamping position by spring action, and an actuating cam for releasing the clamping jaws is arranged under the gripper clamps in an unloading area as well as in a feed area for printed sheets; the actuating cam has a length that corresponds to the length of a plurality of chain links arranged one after another with the gripper clamps fastened thereto, so that all the clamping jaws of the gripper clamps involved in the clamping of a printed sheet can be driven simultaneously in a simple manner by a movement of the actuating cam.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.